Steel cookware is difficult to coat with non-stick coatings such as fluorocarbon coatings. Because of the low thermal conductivity and thermal diffusivity compared to aluminum or copper, steel cookware tends to develop portions hotter than other portions. This leads to softening or deterioration of some parts of the coating faster than other parts.
To minimize rusting, and because of the hardness of steel, it is preferable to use a ceramic frit to prepare the substrate for the fluorocarbon coating rather than grit blasting as is often done with aluminum cookware. However, current fluorocarbon primers generally contain polyamide-imide resins which have undesirable reactions with the frit used on steel substrates. Thus, it is necessary to find fluorocarbon primers which will give desirable results on fritted steel substrates.
U.S. Pat. No. 3,986,993--Vassiliou, issued Oct. 19, 1976, describes a fluorocarbon primer composition which contains 1-10% of an alkyl benzene, preferably toluene. Toluene is a solvent which should be avoided when feasible.
Various patents have described frits that can be fired on steel and frits in combination with fluorocarbon coatings. Included are U.S. Pat. No. 3,850,867--Hartmann, issued Nov. 26, 1974 on an aqueous blend of fluorocarbon resins and frits for use on metal such as aluminum.
Japanese patent publication 52/121,685--Matsushita Electric Industries KK, of Oct. 13, 1977 provides a fluorocarbon coating over a fritted metal substrate; as do British Patent 1,239,217--Welsh Tinplate & Metal Stamping Co., Ltd., published July 14, 1971; and British Patent 1,377,955--VEB Jenaer Glaswerk Schott & Gen., published Dec. 18, 1974.
However, none of the known prior art provides a system which is fully satisfactory for non-stick coating on steel.